Mitochondria has two membranes, one is an internal membrane and the other is an outer membrane. Inner membrane has layered structures, called cristae. The outer membrane covers the organelle. The outer membrane covers the surface of the mitochondrion. These membranes are made of phospholipid layers. Through a series of chemical reactions, mitochondria break down glucose into an energy molecule known as adenosine triphosphate (ATP), which is used to fuel various other cellular processes.